Femto-Gateway, a Cellular Telecommunications Network, and a Method of Identifying a Handover Target Femtocell Base Station

1. A method of identifying a handover target femtocell base station from among multiple femtocell base stations, the method comprising: measuring a characteristic of the handover target femtocell base station to provide a first measured value of the characteristic; then identifying as handover candidate femtocell base stations a first set of femtocell base stations all having that first characteristic value; then changing the characteristic of selected femtocell base stations in the first set; then measuring the characteristic of the handover target femtocell base station to provide a further measured value of the characteristic; then identifying, as a reduced set of handover candidate femtocell base stations, each femtocell base station in the first set having the further measured value of the characteristic; then checking whether the number of femtocell base stations in the reduced set of handover candidate femtocell base stations is one, and upon determining that the number of femtocell base stations in the reduced set is greater than one, taking the reduced set as the first set in repeating the changing, measuring, identifying each femtocell base station and checking.

2. A method according to claim 1 , in which the characteristic is primary scrambling code.

3. A method according to claim 1 , in which the multiple femtocell base stations all lie within a macrocell of a cellular network, and there are fewer primary scrambling code values allocated to the femtocell base stations than the number of femtocell base stations.

4. A method according to claim 1 , in which the measuring steps each comprise the user terminal measuring the characteristic.

5. A method according to claim 1 , in which the characteristic value is forwarded by a serving radio network controller to a femto-gateway in a handover request message.

6. A method according to claim 5 , which includes, upon determining that the number of femtocell base stations in the reduced set is greater than one, the femto-gateway sending a message informing of handover failure to the serving radio network controller.

7. A method according to claim 1 , including a handover of call connection from a macrocell base station to the identified handover target femtocell base station.

8. A method according to claim 1 , in which the characteristic is changed in a first cell of the femtocell base station in response to measurements made by a user terminal, whilst connections to other user terminals are maintained in a second cell of the femtocell base station.

9. A method according to claim 1 , in which in femtocell base stations in which the characteristic is to be changed, connected user terminals are commanded to switch to use of the new characteristic, then the characteristic is changed to the new value.

10. A femto-gateway configured to identify a handover target femtocell base station from among multiple femtocell base stations, the femto-gateway comprising: one or more processors programed to: receive a first measured value of a characteristic of the handover target femtocell base station, identify as handover candidate femtocell base stations a first set of femtocell base stations all having that first characteristic value, change the characteristic of selected femtocell base stations in the first set, receive a further measured value of the characteristic of the handover target femtocell base station, identify as a reduced set of handover candidate femtocell base stations each femtocell base station in the set having the further measured value of the characteristic, check whether the number of femtocell base stations in the reduced set of handover candidate femtocell base stations is one, and, upon determining that the number of femtocell base stations in the reduced set is greater than one, to repeat changing, receiving, identifying each femtocell base station, and checking,taking the reduced set as the first set.

11. A femto-gateway according to claim 10 , in which the multiple femtocell base stations all lie within a macrocell of a cellular network, and there are fewer possible values allocated to the femtocell base stations than the number of femtocell base stations.

12. A femto-gateway according to claim 10 , in which the measured values are received from a the user terminal.

13. A femto-gateway according to claim 10 , wherein the one or more processors is configured to send a message informing of handover failure to a serving radio network controller of the connection for handover upon determining that the number of femtos in the reduced set is greater than one.

14. A network comprising the femto-gateway according to claim 10 , and a femtocell base station in which the characteristic is changed in a first cell of the femtocell base station in response to measurements made by a user terminal, whilst connections to other user terminals are maintained in a second cell of the femtocell base station.

15. A network comprising the femto-gateway according to claim 10 , and a femtocell base station in which the characteristic is to be changed, in which, in use, connected user terminals are commanded to switch to use of the new characteristic value, then the characteristic value is changed to the new value.